[moved] Noise immune cables

[treez]

Hi,
Is shielded coaxial cable for signal transmission, the be-all-and-end-all?

Also, does twisted pair offer more noise immunity than plain bifilar wire pair (not twisted)? (consider overall loop area the same in each case)

Also, when you get shielded coaxial cable, ie shield coating, then ground coating, then centre conductor....why do people put cable ferrites over the whole cable?...surely the cable ferrite should ideally not go over the shield?

 

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Twisted pair exposes both wires equally to an external aggressor signal. hence it equalizes the common mode noise on the differential signal pair. This is why Ethernet cable (UTP) has different twists per inch for each pair of wires, so none of the pairs can expose another pair to a common aggressor signal.

Bifilar wire is used for a different purpose that has nothing to do with common mode noise. I've never dealt with it before so looking it up is is primarily used to cancel out magnetic fields in the pair of wires.

Here is an explanation of common mode signals.
https://www.maximintegrated.com/en/design/technical-documents/tutorials/2/2045.html
Take a look at Table 2 and the rows "Unshielded Parallel Pair" and "Unshielded Twisted Pair" along with the corresponding common mode note.